We are interested in the function, mechanism and regulation of contact-mediated cell interactions in Myxococcus xanthus. Previous work has indicated that developmental autolysis, which occurs during fruiting body formation, is one such interaction and that cell surface polysaccharides or oligosaccharides may serve as a signal coordinating this interaction. We have raised a number of different monoclonal antibodies (MCA) against cell surface antigens of M. xanthus that block normal aggregation and development. Some of these appear to be directed against glycoprotein or polysaccharide antigens. We plan to use Fab' fragments of these blocking MCA 1) to characterize the epitopes of these cell surface antigens; 2) to help clarify the role of a group of amino sugars that seem to serve as developmental signals; 3) to identify signal receptors and 4) to select mutants deficient in signal reception and developmental autolysis. In addition, our laboratory is presently using a number of these developmental-blocking MCA as immunoaffinity reagents to isolate the corresponding cell surface proteins that presumably play a role in cell interactions. These proteins will be sequenced, and will represent the gene products of genes that will be 1) cloned, 2) subjected to site-specific mutagenesis, 3) reintroduced into M. xanthus via P1 transduction, 4) mapped using cotransduction with Tn5 inserts and 5) fused with promoterless lac to study gene expression.